Contaminants in the Canadian Arctic: 5 years of progress in understanding sources, occurrence and pathways

Recent studies of contaminants under the Canadian Northern Contaminants Pro gram (NCP) have substantially enhanced our understanding of the pathways by which contaminants enter Canada's Arctic and move through terrestrial and marine ecosystems there. Building on a previous review (Barrie et al., Arct ic contaminants: sources, occurrence and pathways. Sci Total Environ 1992:1 -74). we highlight new knowledge developed under the NCP on the sources. oc currence and pathways of contaminants (organochlorines, Hg, Pb and Cd, PAHs , artificial radionuclides). Starting from the global scale, we examine emi ssion histories and sources for selected contaminants focussing especially on the organochlorines. Physical and chemical properties, transport process es in the environment (e.g. winds, currents, partitioning), and models are then used to identify, understand and illustrate the connection between the contaminant sources in industrial and agricultural regions to the south an d the eventual arrival of contaminants in remote regions of the Arctic. Wit hin the Arctic, we examine how contaminants impinge on marine and terrestri al pathways and how they are subsequently either removed to sinks or remain where they can enter the biosphere. As a way to focus this synthesis on ke y concerns of northern residents, a number of special topics are examined i ncluding: a mass balance for HCH and toxaphene (CHBs) in the Arctic Ocean; a comparison of PCB sources within Canada's Arctic (Dew Line Sites) with PC Bs imported through long-range transport; an evaluation of concerns posed b y three priority metals - Hg, Pb and Cd; an evaluation of the risks from ar tificial radionuclides in the ocean: a review of what is known about new-ge neration pesticides that are replacing the organochlorines; and a compariso n of natural vs. anthropogenic sources of PAH in the Arctic. The research a nd syntheses provide compelling evidence fur close connectivity between the global emission of contaminants from industrial and agricultural activitie s and the Arctic. For semi-volatile compounds that partition strongly into cold water (e.g. HCH) we have seen an inevitable loading of Arctic aquatic reservoirs. Drastic I-ICI-I emission reductions have been rapidly followed by reduced atmospheric burdens with the result that the major reservoir and transport agent has become the ocean. In the Arctic, it will take decades for the upper ocean to clear itself of HCH. For compounds that partition st rongly onto particles, and for which the soil reservoir is most important ( e.g. PCBs), we have seen a delay in their arrival in the Arctic and some fr actionation toward more volatile compounds (e.g. lower-chlorinated PCBs). D espite banning the production of PCB in the 1970s. and despite decreases of PCBs in environmental compartments in temperate regions, the Arctic presen tly shows little evidence of reduced PCB loadings. We anticipate a delay in PCB reductions in the Arctic and environmental lifetimes measured in decad es. Although artificial radionuclides have caused great concern due to thei r direct disposal on Russian Shelves, they are found to pose little threat to Canadian waters and, indeed, much of the radionuclide inventory can be e xplained as remnant global fallout, which was sharply curtailed in the 1960 s, and waste emissions released under license by the European reprocessing plants. Although Cd pc,ses a human dietary concern both for terrestrial and marine mammals, we find little evidence that Cd in marine systems has been impacted by human activities. There is evidence of contaminant Pb in the A rctic, but loadings appear presently to be decreasing due to source control s (e.g. removal of Pb from gasoline) in Europe and North America. Of the metals, Hg provokes the greatest concern; loadings appear to be incr easing in the Arctic due to global human activities, but such loadings are not evenly distributed nor are the pathways by which they enter and move wi thin the Arctic well understood. (C) 2000 Elsevier Science B.V. All rights reserved.